A new mechanistic framework to predict OCS fluxes from soils
Estimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO<sub>2</sub> cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-04-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/13/2221/2016/bg-13-2221-2016.pdf |
| _version_ | 1818277080205361152 |
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| author | J. Ogée J. Sauze J. Kesselmeier B. Genty H. Van Diest T. Launois L. Wingate |
| author_facet | J. Ogée J. Sauze J. Kesselmeier B. Genty H. Van Diest T. Launois L. Wingate |
| author_sort | J. Ogée |
| collection | DOAJ |
| description | Estimates of photosynthetic and respiratory fluxes at large scales are needed
to improve our predictions of the current and future global CO<sub>2</sub> cycle.
Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and
has been proposed as a new tracer of photosynthetic gross primary
productivity (GPP), as the uptake of OCS from the atmosphere is dominated by
the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that
also catalyses CO<sub>2</sub> hydration during photosynthesis. However soils also
exchange OCS with the atmosphere, which complicates the retrieval of GPP from
atmospheric budgets. Indeed soils can take up large amounts of OCS from the
atmosphere as soil microorganisms also contain CA, and OCS emissions from
soils have been reported in agricultural fields or anoxic soils. To date no
mechanistic framework exists to describe this exchange of OCS between soils
and the atmosphere, but empirical results, once upscaled to the global scale,
indicate that OCS consumption by soils dominates
OCS emission and its contribution to the atmospheric budget is large, at about one third
of the OCS uptake by vegetation, also with a large uncertainty. Here, we
propose a new mechanistic model of the exchange of OCS between soils and the
atmosphere that builds on our knowledge of soil CA activity from CO<sub>2</sub>
oxygen isotopes. In this model the OCS soil budget is described by a
first-order reaction–diffusion–production equation, assuming that the
hydrolysis of OCS by CA is total and irreversible. Using this model we are
able to explain the observed presence of an optimum temperature for soil OCS
uptake and show how this optimum can shift to cooler temperatures in the
presence of soil OCS emission. Our model can also explain the observed
optimum with soil moisture content previously described in the literature as
a result of diffusional constraints on OCS hydrolysis. These diffusional
constraints are also responsible for the response of OCS uptake to soil
weight and depth observed previously. In order to simulate the exact OCS
uptake rates and patterns observed on several soils collected from a range of
biomes, different CA activities had to be invoked in each soil type, coherent
with expected physiological levels of CA in soil microbes and with CA
activities derived from CO<sub>2</sub> isotope exchange measurements, given the
differences in affinity of CA for both trace gases. Our model can be used to
help upscale laboratory measurements to the plot or the region. Several
suggestions are given for future experiments in order to test the model
further and allow a better constraint on the large-scale OCS fluxes from both
oxic and anoxic soils. |
| first_indexed | 2024-12-12T22:55:51Z |
| format | Article |
| id | doaj.art-ac1bf58bc34a4eb3a735bd9352aa4cff |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-12T22:55:51Z |
| publishDate | 2016-04-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-ac1bf58bc34a4eb3a735bd9352aa4cff2022-12-22T00:08:56ZengCopernicus PublicationsBiogeosciences1726-41701726-41892016-04-011382221224010.5194/bg-13-2221-2016A new mechanistic framework to predict OCS fluxes from soilsJ. Ogée0J. Sauze1J. Kesselmeier2B. Genty3H. Van Diest4T. Launois5L. Wingate6INRA, UMR 1391 ISPA, 33140 Villenave d'Ornon, FranceINRA, UMR 1391 ISPA, 33140 Villenave d'Ornon, FranceMax Planck Institute for Chemistry, Biogeochemistry Department, Mainz, GermanyCNRS/CEA/Aix-Marseille University, UMR 6191 BVME, Saint-Paul-lez-Durance, FranceMax Planck Institute for Chemistry, Biogeochemistry Department, Mainz, GermanyINRA, UMR 1391 ISPA, 33140 Villenave d'Ornon, FranceINRA, UMR 1391 ISPA, 33140 Villenave d'Ornon, FranceEstimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO<sub>2</sub> cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic gross primary productivity (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO<sub>2</sub> hydration during photosynthesis. However soils also exchange OCS with the atmosphere, which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere, but empirical results, once upscaled to the global scale, indicate that OCS consumption by soils dominates OCS emission and its contribution to the atmospheric budget is large, at about one third of the OCS uptake by vegetation, also with a large uncertainty. Here, we propose a new mechanistic model of the exchange of OCS between soils and the atmosphere that builds on our knowledge of soil CA activity from CO<sub>2</sub> oxygen isotopes. In this model the OCS soil budget is described by a first-order reaction–diffusion–production equation, assuming that the hydrolysis of OCS by CA is total and irreversible. Using this model we are able to explain the observed presence of an optimum temperature for soil OCS uptake and show how this optimum can shift to cooler temperatures in the presence of soil OCS emission. Our model can also explain the observed optimum with soil moisture content previously described in the literature as a result of diffusional constraints on OCS hydrolysis. These diffusional constraints are also responsible for the response of OCS uptake to soil weight and depth observed previously. In order to simulate the exact OCS uptake rates and patterns observed on several soils collected from a range of biomes, different CA activities had to be invoked in each soil type, coherent with expected physiological levels of CA in soil microbes and with CA activities derived from CO<sub>2</sub> isotope exchange measurements, given the differences in affinity of CA for both trace gases. Our model can be used to help upscale laboratory measurements to the plot or the region. Several suggestions are given for future experiments in order to test the model further and allow a better constraint on the large-scale OCS fluxes from both oxic and anoxic soils.http://www.biogeosciences.net/13/2221/2016/bg-13-2221-2016.pdf |
| spellingShingle | J. Ogée J. Sauze J. Kesselmeier B. Genty H. Van Diest T. Launois L. Wingate A new mechanistic framework to predict OCS fluxes from soils Biogeosciences |
| title | A new mechanistic framework to predict OCS fluxes from soils |
| title_full | A new mechanistic framework to predict OCS fluxes from soils |
| title_fullStr | A new mechanistic framework to predict OCS fluxes from soils |
| title_full_unstemmed | A new mechanistic framework to predict OCS fluxes from soils |
| title_short | A new mechanistic framework to predict OCS fluxes from soils |
| title_sort | new mechanistic framework to predict ocs fluxes from soils |
| url | http://www.biogeosciences.net/13/2221/2016/bg-13-2221-2016.pdf |
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